Optical displacement sensor for infusion devices

ABSTRACT

An optical sensor for a delivery device having a piston that displaces a substance, such as a fluid, from a reservoir. The optical sensor has a light source and a detector array for imaging encoding features disposed along a plunger rod coupled to the piston. By virtue of the pattern of encoding features, an absolute position of the plunger rod relative to a fiducial position may be determined uniquely. Thus, the volume of fluid remaining in the reservoir, the rate of fluid delivery, and proper loading of the reservoir may be accurately ascertained. Additionally, the encoding may serve to uniquely identify a version of the reservoir which may be supplied in various versions corresponding, for example, to differing concentrations of a therapeutic agent to be dispensed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/959,636, filed Apr. 23, 2018, which is a continuation of U.S.application Ser. No. 14/047,488, filed Oct. 7, 2013, which is acontinuation of U.S. application Ser. No. 12/395,862, filed Mar. 2,2009, which is a continuation of U.S. application Ser. No. 10/625,792,filed Jul. 23, 2003, which claims priority to U.S. ProvisionalApplication 60/398,259, filed Jul. 24, 2002, each of which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention pertains to optical sensors for monitoring thesource and/or amount of a substance, such as a medicinal agent,delivered by a delivery device.

BACKGROUND ART

Devices, such as pumps or manual pens, used for delivering substances,such as drugs or insulin, from a local reservoir into the body of apatient are prone to problems that may impede the intended delivery rateof the substance. Such problems may include clogging, mechanicalsticking, or misidentification of the administered substance. It is thusdesirable that the source of the delivered substance be positivelyidentified by the delivery device, that the proper loading of thesubstance reservoir be verified, that the instantaneous volume ofsubstance in the reservoir be ascertainable, and that both the rate ofdelivery and the precise volume of remaining liquid be accuratelymonitored. Prior use of an optical monitor for similar applications,such as described in U.S. Pat. No. 4,498,843 to Schneider, et al., hasbeen limited to measurement of delivery rate. It is, furthermore,desirable that the aforesaid functions be provided both accurately andcost effectively.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the invention, there isprovided a displacement sensor for a dispensing device of the type thathas a translating piston. The sensor has a plunger rod coupled to thepiston, and the plunger rod has an encoded pattern of encoding features.A light source illuminates the encoded pattern and a detector arraydetects light from the illuminated encoded pattern and generates adetector signal such that, on the basis of the detected signal, aprocessor determines a displacement of the plunger rod relative to afiducial reference position. The delivery rate of a substance dispensedby the device may also be determined. Additionally, the encoded patternmay serve to identify a reservoir type characterized, for example, by adistinct concentration of a therapeutic agent to be delivered by thedispensing device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the fundamental constituents of a prior art medical fluidpump;

FIG. 2 is a schematic depiction of an optical linear encoder fordelivery of a liquid agent in accordance with preferred embodiments ofthe present invention;

FIG. 3 is a perspective view of a medical fluid pump including anoptical linear encoder in accordance with an embodiment of the presentinvention; and

FIG. 4 is an exploded view of an embodiment of an optical linear encoderin accordance with the invention as applied to a medical fluid pump.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Major components of a pump for delivering a therapeutic agent to thebody of a patient are described with reference to FIG. 1. A medicationreservoir 11, typically cylindrical in shape, is retained within ahousing 16 and contains a liquid agent to be delivered to a patient viaa delivery tube 18 and a hypodermic needle (not shown). The liquid agentcontained within the reservoir is impelled out of the reservoir at adetermined rate by linear motion of a piston 30 along a direction 8coaxial with the axis of the reservoir. The piston is driven by aplunger rod 12 that is driven, in turn, at a prescribed rate, by a motor(not visible) coupled to a screw drive 14 via a gear reduction drive. Itis to be understood that the present invention may advantageously beapplied for delivery devices other than pumps, such as insulin pens, aswell as for the delivery of various fluids or other substances that maybe medicating agents or other substances. The description of a pump andin terms of delivery of a therapeutic agent to a patient is withoutlimitation and by way of example only. Embodiments of the presentinvention may also advantageously be applied, for example, for deliveryof purification agents into a water supply. The fluid to be delivered istypically a liquid, however the delivery of other substances is alsowithin the scope of the present invention as described herein and asclaimed in any appended claims.

The rate at which the pump motor is driven in order to impel the pistonto deliver the liquid agent at a prescribed rate is governed by aprocessor on the basis of the cross section of the reservoir (i.e., thevolume of agent expelled per unit linear motion of the piston) and theconcentration of agent within the fluid contained in the reservoir.

In accordance with preferred embodiments of the present invention, anoptical linear encoder is used to determine both the absolute positionand rate of motion of the plunger rod. Additionally, since the reservoirand piston may be supplied to the user as an integral unit, additionalinformation may be encoded on the plunger rod, as described in greaterdetail below.

It is desirable, in particular, that four functionalities be provided bya sensor used in conjunction with fluid delivery:

a. monitoring delivery accuracy;

b. identifying a characterizing feature of the reservoir (such as to itscontents);

c. determining the volume of fluid remaining in the reservoir; and

d. verifying proper loading of the reservoir.

It is particularly advantageous if, as in accordance with a preferredembodiment of the present invention, all of the above functionalitiesmay be provided by a single sensor.

If, as in preferred embodiments of the present invention, the reservoiridentification is associated with the concentration in the fluid of adrug to be delivered by the infusion device, then a programmed dose maybe converted into a linear distance.

In preferred embodiments, transmission-type encoding is employed,however, any analogous reflection-type encoding is within the scope ofthe invention. Referring to FIG. 2, piston 30 is driven along axis 32 soas to impel the liquid contents of reservoir 34 out orifice 36. Piston30 is propelled by plunger rod 38, which advances as lead screw 40 isrotated. In the preferred embodiments of transmission-type encoding, alight source 42 and detector 44 are disposed on opposite sides ofplunger rod 38. As used herein, the term “detector” may refer, as thecontext demands, to an array of detectors. The detector or detectorarray may also be referred to, herein, as an “image sensor” or an “imagearray.” The term “detector assembly” may refer to a detector or array ofdetectors along with associated preamplification and signal-conditioningelectronics. Plunger rod 38 is encoded, in such embodiments, by features46 that may be recognized by detector 44.

In accordance with one embodiment of the invention, encoding features 46are slots orthogonal to the axis of travel 32 of the piston are scoredinto plunger rod 38. In alternate embodiments, round (or otherwiseshaped) holes, or slots parallel to axis 32, wedges, or otherlight-transmitting features may be employed, all the above providedsolely for purposes of example and without limitation. Slots 46 or otheroptically transmissive features may be fully optically transmissive ormay, alternatively, modulate the some detectable characteristic of light(designated by dashed lines 48) transmitted between source 42 anddetector 44. Transmissive features 46 may thus employ filters (ofneutral density or otherwise), thereby modulating the intensity and/orspectral characteristics of the transmitted light, or may employpolarizers or retardation plates, thereby modulating the polarization orphase of the transmitted light. All such techniques for encodingtransmitted light are within the scope of the present invention asdescribed herein and as claimed in any appended claims.

In accordance with preferred embodiments of the present invention,detector 44 advantageously spans merely a portion of the region ofplunger rod, as described in greater detail below, however any relativesizes of the detector 44 and plunger rod 38 are within the scope of thepresent invention.

The path of light from light source 42 to detector 44 may be one ofdirect transmission through plunger rod 38 as shown. Alternatively,encoding 46 may be detected in reflection by suitable placement ofdetector 44 on the same side of plunger rod 38 as light source 42. Lightsource 42 may be an array of light-emitting-diodes (LEDs), in which casediffuser 50 may be employed. Other sources of diffuse light, such aselectro-luminescent light sources may also be employed. Diffuser 50 mayinclude multiple diffusion stages, as shown. Illumination may also beprovided by undiffused light. Illumination may be transmitted throughencoding 46 directly onto detector 44, as shown, or, in otherembodiments of the invention, a reflective light path or transfer ofillumination pattern via optical fibers or other light pipes may beemployed. Intervening optics such as a lens, microchannel plate, etc.,may also be provided within the optical path, within the scope of thepresent invention.

A housing 60 for embodying the substance dispenser components of FIG. 2is shown in perspective view in FIG. 3. Motor drive 62 is hidden fromview but shown as a dashed component. Reservoir 34, with plunger rod 38in extension therefrom, is shown prior to insertion into the housing.The exploded view of FIG. 4 shows drive module 70, containing drivemotor 62 and reservoir barrel 72, light source module 42, diffuser 50,detector 44

Detector 44 may be comprised of multiple detector resolving elements,and may be realized as a CMOS linear image sensor, for example, or acharge-coupled device (CCD) array, for another example. Many formats maybe employed advantageously. Within the scope of the present invention,the detector elements may be linearly or two-dimensionally arrayed, andsuch arrays may be realized, if design considerations so require, byboth linear and lateral stacking of detector arrays.

The image formed on detector 44 is analyzed, by directing the outputsignal of detector 44, via analog-to-digital converter 54, to processor56, in accordance with various algorithms to be discussed in detailbelow. Pixel size and number are optimized with respect to resolutionand resources demanded of processor 56.

By means of employing an encoding pattern that does not repeat,positioning of the moveable plunger rod with respect to the fixedoptical assembly (taken to comprise both the illuminating and detectingoptics) may advantageously be determined absolutely. Alternatively, theslot pattern or other encoding pattern may be repeated one or moretimes, thereby allowing translation to be encoded over large traveldistances. In embodiments wherein the encoding pattern defines anon-unique current position of the plunger rod, plunger rod 38 may bedriven to a fiducial position 52, such as a limit stop, in order toestablish a reference from which to count repeats and to establish anabsolute present position of the plunger rod relative to the fiducialposition.

In preferred embodiments of the invention, detector 44 is realized as a512-pixel linear array, with pixel resolution of approximately 16. mu.m.Detector 44 is positioned along and parallel to the line of travel ofplunger rod 38, beginning substantially at the end of lead screw 40.Particularly when focusing optics are not employed, it is preferred thatdetector 44 should be positioned in close proximity to plunger rod 38.

In a preferred embodiment of the invention, the spacing of plunger rodslots 46 is chosen in such a manner that any two adjacent spaces form aunique sequence. Additionally, the sum of the lengths of any two spacesis always greater than the distance between any two adjacent slots,thus, in case a slot becomes unintentionally blocked, the anomaly may bedetected and not mistaken for another absolute position. Additionally,it is provided that either three or more slots are visible to the imagesensor at any one time, or else the end of the rod and at least one slotare visible to the image sensor at any given time.

The three versions of slot spacings, given in inches in Table I, meetthe preferred criteria discussed in the foregoing paragraph. The spacingof any two adjacent spaces may be coded to uniquely define a version ofthe reservoir, so that different concentrations of medicinal agent maybe supplied and distinguished. Characteristics of the reservoir versionthat may be identified in this manner include, without limitation, theinner diameter of the reservoir, and the composition (plastic or glass,for example) of the wall of the reservoir. Additionally, the distancebetween the end of the plunger rod and the last slot may uniquelyidentify a reservoir version, so that, in case no more than one slot iswithin the field of view of the image sensor, the reservoir version maybe uniquely identified.

TABLE I Slot To Slot Distance (inches) Slot 1 Slot 2 Slot 3 Slot 4 Slot5 Slot 6 Slot 7 Slot 8 Slot 9 Slot 10 to to to to to to to to to toVersion Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Slot 7 Slot 8 Slot 9 Slot 10end #1 0.084 0.096 0.084 0.084 0.060 0.096 0.108 0.060 0.060 0.110 #20.072 0.060 0.072 0.096 0.096 0.072 0.084 0.108 0.072 0.095 #3 0.0600.108 0.096 0.060 0.084 0.072 0.072 0.108 0.084 0.080

To create an image, all pixels of detector 44 are reset. Then lightsource 42 is flashed such that light is emitted for a specified durationof time. Variable-duration exposure times may be employed, such thatlonger times are used when slots are being viewed, whereas shorter timesare used when the end of the plunger rod is being viewed. Exposure timesof 5 ms for slots and 0.7 ms for the end of the rod have been found tobe satisfactory. The signal from detector 44 is read, with values foreach pixel stored by processor 56 in an array and interpreted using oneor more algorithms.

In the embodiment to which Table I refers, there is a small portion ofthe travel where only two slots are visible (9 and 10) as well as theend of the rod. The normal means of identifying the syringe using twoadjacent spaces cannot be used since only a single spacing is available.The alternate means of identifying the syringe using the distancebetween the end of rod and the last slot cannot be used because the endis too close to the edge of view to be detected using the sliding windowalgorithm. Thus a third means of identifying the syringe is used whenonly two slots are visible and the end of the rod position cannot bemeasured but is visible. This third method relies on a uniqueslot-9-to-slot-10 spacing.

In accordance with one exposure procedure, the light is left on. Then,the detector reads and resets each pixel in sequence at a specific clockrate. The array is then read twice, the first read serving to reset thepixels. The second read of each pixel thus occurs “n” times the clockperiod since that pixel was reset.

In a preferred mode of operation, measurements of plunger rod positionare made once per basal step of the piston, during delivery of a bolus,and during priming. In between measurements, image sensor power may beremoved, since the position determination is absolute.

In accordance with embodiments of the invention, various algorithms maybe employed in order to detect the position of transmitted light peaksto within specified resolution. One Peak Detection Algorithm employs asliding window split into two equal halves. The values of pixels in eachhalf are summed, and the sums subtracted from each other. The differencebetween the signals in the two halves is calculated for all possiblepositions of the sliding window, giving a measure of the slope of theintensity curve. As zeroes occur at local extrema, whether peaks orvalleys, the sign of the difference value as the zero point isapproached is used to distinguish between these two cases. Other peakand edge identifying algorithms are within the scope of the presentinvention. Movement of the peaks may be used to track the accuracy ofplunger rod movement and thus delivery of the liquid agent being drivenout of the reservoir.

In accordance with further embodiments of the invention, the spacingbetween slots can be resolved to finer increments than the pitch ofdetector 44 by storing the ND pixel values in a software array withpower-of-2 more elements than the sensor array. For example, resolutionwould be increased eightfold if a 512 pixel image was stored in a 4096element software array. This is done by storing the 1.sup.st sensorarray value in each of the 1.sup.st eight software array elements. The2.sup.nd sensor array value is stored in each of the next eight softwarearray elements, and so on.

Alternatively, by reading every n.sup.th pixel, where n is a power of 2,and storing these values in a software array with the same number ofelements as the sensor array, image read times can be decreased withoutadversely affecting the slot to slot measurement resolution.

Having thus described various illustrative embodiments of the presentinvention, some of its advantages and optional features, it will beapparent that such embodiments are presented by way of example only andare not by way of limitation. It is to be understood that the teachingsof the present invention may be applied to the metered delivery offluids for other applications, such as the delivery of chemicals to asupply of potable water, to name merely a single example. Those skilledin the art could readily devise alternations and improvements on theseembodiments, as well as additional embodiments, without departing fromthe spirit and scope of the invention. All such modifications are withinthe scope of the invention as claimed.

What is claimed is:
 1. A medical fluid dispensing apparatus comprising:a piston having a motion wherein the piston causes the medical fluid tobe impelled out of the medical fluid dispensing apparatus at adetermined delivery rate; and an optical sensor, wherein the opticalsensor is configured to determine the position of the piston, relativeto a fiducial position, during delivery.
 2. The apparatus of claim 1,further comprising a reservoir and a motor, wherein the piston is drivenby the motor, at a prescribed rate, to impel the medical fluid out ofthe reservoir.
 3. The apparatus of claim 1 further comprising a plungerrod coupled to the piston, the plunger rod bearing an encoded pattern ofat least one encoding feature, wherein the encoding feature include atleast one optically transmissive feature.
 4. The apparatus of claim 3further comprising an illumination source, the illumination sourcelocated wherein light from the illumination source is transmitted to theat least one optically transmissive feature.
 5. The apparatus of claim 3further comprising at least one detector for detecting light transmittedto the at least one encoding feature.
 6. The apparatus of claim 5wherein the at least one encoding feature is a slot scored into theplunger rod.
 7. The apparatus of claim 5 wherein the at least oneencoding feature is an aperture.
 8. The apparatus of claim 1 furthercomprising a plunger rod coupled to the piston, the plunger rod bearingan encoded pattern of encoding features, wherein the encoding featurescomprising a plurality of optically transmissive features.
 9. Theapparatus of claim 8 wherein the spacing of the encoding features fromone another defines spaces between such that any two adjacent spacesform a unique sequence.
 10. The apparatus of claim 1 further comprisinga plunger rod coupled to the piston, the plunger rod bearing an encodedpattern of at least one encoding feature, wherein the encoding featureinclude at least one reflective feature.
 11. The apparatus of claim 10further comprising an illumination source, the illumination sourcelocated wherein light from the illumination source is transmitted to theat least one reflective feature.
 12. The apparatus of claim 10 furthercomprising at least one detector for detecting light reflected by the atleast one encoding feature.
 13. The apparatus of claim 1 furthercomprising a plunger rod coupled to the piston, the plunger rod bearingan encoded pattern of encoding features, wherein the encoding featurescomprising a plurality of reflective features.
 14. The apparatus ofclaim 13 wherein the spacing of the encoding features from one anotherdefines spaces between such that any two adjacent spaces form a uniquesequence.
 15. A medical fluid dispensing apparatus comprising: a pistonhaving a motion wherein the piston causes the medical fluid to beimpelled out of the medical fluid dispensing apparatus at a determineddelivery rate; a plunger rod coupled to the piston, the plunger rodbearing an encoded pattern of at least one encoding feature, wherein theencoding feature includes at least one reflective feature; and anoptical sensor, wherein the optical sensor is configured to determinethe position of the piston, relative to a fiducial position, duringdelivery.
 16. The apparatus of claim 15, further comprising a reservoirand a motor, wherein the piston is driven by the motor, at a prescribedrate, to impel the medical fluid out of the reservoir.
 17. The apparatusof claim 15 further comprising an illumination source, the illuminationsource located wherein light from the illumination source is transmittedto the at least one reflective feature.
 18. The apparatus of claim 17further comprising at least one detector for detecting light reflectedby the at least one encoding feature.
 19. The apparatus of claim 15further comprising wherein the plunger rod comprising a plurality ofreflective features.
 20. The apparatus of claim 19 wherein the spacingof the encoding features from one another defines spaces between suchthat any two adjacent spaces form a unique sequence.